Molybdenum is an increasingly important material and is used for various industrial and scientific purposes. These purposes range from imparting strength in metal alloys to use as a chemical catalyst. Likewise, molybdenum compositions are highly suitable for the production of a wide variety of products, including electrical contacts, electrical filaments, colloidal lubricant additives, and other diverse products.
Molybdenum does not occur as a free element in nature. In nature it can be found in various common forms, such as in ore in the form of molybdenite (MoS2). Molybdenite generally forms a relatively small percentage of the ore in which it is found. Typically, molybdenite ore consists of silicified granite compositions having deposits of soft, black, and hexagonal MoS2 crystalline structures widely dispersed therein. These materials are found in an average concentration of only about less than 1% by weight of the entire ore body. Accordingly, significant process steps are typically required in order to recover molybdenum from ore.
In view of its increasing industrial and scientific importance, substantial research activity has been devoted to the development of improved methods for the beneficiation of MOS2-containing ore products. Normally, MoS2 derived from molybdenite ore is converted by oxidization to various oxides of molybdenum, followed by further processing in order to obtain a purified molybdenum oxide product consisting primarily of molybdenum trioxide (MoO3).
The molybdenite ore may be initially subjected to a physical grinding process in which the ore is reduced in size to a plurality of small particles. The ore particles are then further treated to remove the desired MoS2. This step may be accomplished using a variety of techniques, including organic flotation extraction procedures. As a result, the desired MoS2 may be effectively separated from ore-based waste materials (conventionally known as “gangue”) which consist primarily of silica-containing by-products. Specifically, the desired MoS2 compositions will, by control of the surface chemistry within the flotation unit, be readily isolated in the flotation froth. Many variations and alternatives exist in connection with the isolation of MoS2 from the ore, with the selected procedure depending on the type and grade of ore to be processed.
Once isolated, MoS2 may converted (oxidized) to form MoO3 by forming a slurry or suspension of MoS2 in water and thereafter heating the slurry in a pressure leach vessel. During the heating process, an oxygen atmosphere is maintained within the vessel. As a result, MoO3 is generated in accordance with one or more variations of the following exothermic reaction.MoS2+4.5O2(g)+2H2O→MoO3+2H2SO4 
Several patents and other literature have taught numerous processes and systems for carrying out one or more variations on the above reaction to greater or lesser degrees of completion. Some of the patents which discuss this type of process include: U.S. Pat. No. 4,046,852 to Vertes, et al., entitled “Purification Process for Technical Grade Molybdenum Oxide”; U.S. Pat. No. 4,165,362 to Reynolds, entitled “Hydrometallurgical Processing of Molybdenite Ore Concentrates”; U.S. Pat. No. 4,379,127 to Bauer, et al., entitled “Method of Recovering Molybdenum Oxide”; U.S. Pat. No. 4,444,733 to Laferty, et al., entitled “Process for Recovering Molybdenum and Copper From Sulfide Concentrates”; U.S. Pat. No. 4,478,698 to Wilkomirsky, et al., entitled “Process For Recovering Copper and Molybdenum From Low Grade Copper Concentrates”; U.S. Pat. No. 4,512,958 to Bauer, et al., entitled “Method of Recovering Molybdenum Oxide”; U.S. Pat. No. 5,804,151 to Sweetser, et al., entitled “Process For Autoclaving Molybdenum Disulfide”; and U.S. Pat. No. 5,820,844 to Khan, et al., entitled “Method for the Production of A Purified MoO3 Composition.”
Many of these patents and other publications focus on the oxidation reaction that converts some or all of the MoS2 to MoO3 or other molybdenum oxides, which other oxides may be referred to as lesser molybdenum oxides. While the oxidation reaction is an important step in the preparation of molybdenum oxide from molybdenum-containing ore, the process for obtaining usable molybdenum typically includes numerous post-oxidation reaction steps that are important to the overall efficiency of the process.
U.S. Pat. No. 6,730,279, to Balliett et al., entitled “Production of Pure Molybdenum Oxide from Low Grade Molybdenite Concentrates,” which issued on May 4, 2004, illustrates possible post-oxidation steps. For example, a process illustrated in Balliett et al. includes an oxidation step, followed by a separation step to separate the molybdenum oxide material from a centrate. The centrate is sent to an optional amine solvent-extraction process operated to produce a two-phase mixture having a molybdenum-loaded organic phase and an aqueous phase. The organic phase is stripped with concentrated sulfuric acid, at a pH less than about 3 and the recovered molybdenum values are recycled back to the oxidation step. Although the inventors purport that this process works, some results indicate otherwise. Furthermore, use of concentrated sulfuric acid to strip the organic material is detrimental to most processing equipment and thus increases operating costs of molybdenum recovery systems and processes. Accordingly, improved methods and systems for efficiently obtaining molybdenum oxide from molybdenite concentrates that do not employ sulfuric acid stripping are desired.